Obviously, with Lugers, there is a wealth of proofs and marks, both factory and unit, which require a small library. The Jeff Noll book sounds like what the doctor ordered...military unit markings do have an immediate appeal. I did get The Luger Story by John Walter, so at least I have some basic reference.
A local gun shop has 8 or 9 good looking Lugers from the estate of a recently deceased collector inculding the 1916 DWM P.K. 159. Of course, they are all over-priced, so I expect that I have some time, but I still feel under the gun to learn more.
Will check back with you later.